1. Field of the Invention
This invention relates to a granulating and coating technique, and more particularly to a technique effective in use for granulating, coating, drying and the like of a powdery or granular material having a relatively minute particle diameter.
2. Related Art Statement
As the granulating and coating technique of the type described, there has been such a technique that spray nozzles for supplying a raw powdery or granular material as being an article to be coated and a coating liquid as being a coating material are opposed to each other in an apparatus such as described in European Patent No. 0179943.
However, in the above-described technique, the article to be coated and the coating material collide with each other in directions opposed to each other. And, in a system of colliding in the opposed directions, due to an imbalance between the sprayings, either one of the two collision force tends to be stronger than that of the other.
For example, when the blow-out force of the coating liquid is stronger, the coating material adheres to the inner wall surface opposed thereto and is solidified thereat in the apparatus. In that case, before the coating material solidifys, the article to be coated may adhere onto the coating material and be accumulated thereat.
Furthermore, there may occur such a disadvantage that, due to the imbalance between the blow-out forces and/or the blow-out flow rates, the coating liquid is solidified into particles without adhering to and being coated on the article to be coated; so-called "spray dry phenomenon".
Further, the inventors of the present invention have found that, in the normal granulating and coating technique such as U.S. Pat. No. 4,556,175 in which only the hot air is supplied as the drying air stream, the above-described "spray dry phenomenon" may occur even when the spray nozzles are not opposed to each other.